Dopamine is a monoamine neurotransmitter that plays a critical role in the function of the hypothalamic-pituitary-adrenal axis and in the integration of information in sensory, limbic, and motor systems. The primary mechanism for termination of dopamine neurotransmission is through reuptake of released dopamine by Na+/Cl−-dependent plasma membrane transporters (Hoffman et al., 1998, Front. Neuroendocrinol. 19(3):187–231). Depending on the surrounding ionic conditions, the dopamine transporter can function as a mediator of both inward directed dopamine transport (i.e., “reuptake”) and outward directed dopamine transport (i.e., “release”). The functional significance of the dopamine transporter is its regulation of dopamine neurotransmission by terminating the action of dopamine in a synapse via reuptake (Hitri et al., 1994, Clin. Pharmacol. 17:1–22).
Attention deficit disorder is a learning disorder involving developmentally inappropriate inattention with or without hyperactivity. The primary signs of attention deficit disorder are a patient's inattention and impulsivity. Inappropriate inattention causes increased rates of activity or reluctance to participate or respond. A patient suffering from attention deficit disorder exhibits a consistent pattern of inattention and/or hyperactivity-impulsivity that is more frequent and severe than is typically observed in individuals at a comparable level of development. (See, e.g., U.S. Pat. No. 6,121,261 to Glatt et al.).
Patients having Parkinson's disease display jittery movements of the limbs, head, and jaw. Parkinson's disease is associated with bradykinesia, rigidity and falling (Stacy et al., 1996, Am. Fam. Phys. 53:1281–1287). The movement disturbances observed in Parkinson's disease patients result from degeneration of dopamine neurons, loss of nerve terminals, and dopamine deficiency. It is hypothesized that the cause of the degeneration of the dopamine neurons results from apoptosis resulting from increased levels of cytokines (Nagatsu et al., 2000, J. Neural Transm. Suppl. 60:277–290). Abnormalities in the dopamine transporter have been implicated in Parkinson's disease (Hitri et al., 1994, Clin. Neuropharmacol. 17:1–22). Symptoms of Parkinson's disease can be attenuated by compounds like pergolide which mimics the actions of dopamine or by compounds that inhibit dopamine metabolism (e.g., carbidopa) or by dopamine precursors (e.g., L-DOPA± carbidopa).
Appetite suppression is a reduction, a decrease or, in cases of excessive food consumption, an amelioration in appetite. This suppression reduces the desire or craving for food. Appetite suppression can result in weight loss or weight control as desired. Appetite suppression can regulate food intake through drug administration directed to one or more systems known to play a role in food digestion. See, for example, Sullivan et al., “Mechanisms of Appetite Modulation By Drugs,” Federation Proceedings, Volume 44, No. 1, Part 1, pages 139–144 (1985). Methods for controlling appetite suppression include the regulation of serotonin level, thermogenesis and the inhibition of lipogenesis. (See e.g., U.S. Pat. No. 5,911,992 to Braswell et al.).
Depression is one of the most common of the mental illnesses, having a morbidity rate of over 10% in the general population. Depression is characterized by feelings of intense sadness, despair, mental slowing, loss of concentration, pessimistic worry, agitation, and self-deprecation (Harrison 's Principles of Internal Medicine 2490–2497 (Fauci et al. eds., 14th ed. 1998)). Depression can have physical manifestations including insomnia, hypersomnia, anorexia, weight loss, overeating, decreased energy, decreased libido, and disruption of normal circadian rhythms of activity, body temperature, and endosine functions. In fact, as many as 10% to 15% of depressed individuals display suicidal behavior. R. J. Baldessarini, Drugs and the Treatment of Psychiatric Disorders: Depression and Mania, in Goodman and Gilman's The Pharmacological Basis of Therapeutics 431 (9th ed. 1996). Anhedonia is one of the principal (core) symptoms of depression. Dopamine pathways have been linked to pleasure seeking behaviors, and strategies to increase synaptic concentrations of dopamine have been proposed as antidepressant therapies. (See e.g., D'Aquila et al., 2000, Eur. J. Pharmacol. 405:365–373).
Obesity is commonly referred to as a condition of increased body weight due to excessive fat. Drugs to treat obesity can be divided into three groups: (1) those that decrease food intake, such as drugs that interfere with monoamine receptors, such as noradrenergic receptors, serotonin receptors, dopamine receptors, and histamine receptors; (2) those that increase metabolism; and (3) those that increase thermogenesis or decrease fat absorption by inhibiting pancreatic lipase (Bray, 2000, Nutrition 16:953–960 and Leonhardt et al., 1999, Eur. J. Nutr. 38:1–13).
Many drugs can cause physical and/or psychological addiction. Those most well known drugs include opiates, such as heroin, opium and morphine; sympathomimetics, including cocaine and amphetamines; sedative-hypnotics, including alcohol, benzodiazepines and barbiturates; and nicotine, which has effects similar to opioids and sympathomimetics. Drug addiction is characterized by a craving or compulsion for taking the drug and an inability to limit its intake. Additionally, drug dependence is associated with drug tolerance, the loss of effect of the drug following repeated administration, and withdrawal, the appearance of physical and behavioral symptoms when the drug is not consumed. Sensitization occurs if repeated administration of a drug leads to an increased response to each dose. Tolerance, sensitization, and withdrawal are phenomena evidencing a change in the central nervous system resulting from continued use of the drug. This change motivates the addicted individual to continue consuming the drug despite serious social, legal, physical and/or professional consequences. (See, e.g., U.S. Pat. No. 6,109,269 to Rise et al.). Cocaine addiction remains one of the major health problems in the United States. Fundamental studies from many laboratories have shown that cocaine blocks the uptake of dopamine from the synaptic cleft of the dopamine transporter (Kreek, 1996, J. Addict. Dis. 15:73–96). For example, the inhibition action of cocaine on reuptake of released dopamine, however, does not fully explain the development and maintenance of addictive behavior. Coexistence of functionally antagonistic, inhibition actions of cocaine on the dopamine release and reuptake of the released dopamine might be responsible for fluctuations in dopamine transmission (Kiyatkin, 1994, Int. J. Neurosci. 78:75–101).
Certain pharmaceutical agents have been administered for treating addiction. U.S. Pat. No. 5,556,838 to Mayer et al. discloses the use of nontoxic NMDA-blocking agents co-administered with an addictive substance to prevent the development of tolerance or withdrawal symptoms. U.S. Pat. No. 5,574,052 to Rose et al. discloses co-administration of an addictive substance with an antagonist to partially block the pharmacological effects of the substance. U.S. Pat. No. 5,075,341 to Mendelson et al. discloses the use of a mixed opiate agonist/antagonist to treat cocaine and opiate addiction. U.S. Pat. No. 5,232,934 to Downs discloses administration of 3-phenoxypyridine to treat addiction. U.S. Pat. Nos. 5,039,680 and 5,198,459 to Imperato et al. disclose using a serotonin antagonist to treat chemical addiction. U.S. Pat. No. 5,556,837 to Nestler et. al. discloses infusing BDNF or NT-4 growth factors to inhibit or reverse neurological adaptive changes that correlate with behavioral changes in an addicted individual. U.S. Pat. No. 5,762,925 to Sagan discloses implanting encapsulated adrenal medullary cells into a patient's central nervous system to inhibit the development of opioid intolerance. Bupropion has dopamine reuptake inhibition properties and is used to treat nicotine addiction.
Dopaminergic reward pathways have been implicated in disorders resulting from addictive behaviors. Variants of the dopamine D2 receptor gene have been associated with alcoholism, obesity, pathological gambling, attention deficit hyperactivity disorder, Tourette syndrome, cocaine dependence, nicotine dependence, polysubstance abuse, and other drug dependency (Noble, 1994, Alcohol Supp. 2:35–43 and Blum et al., 1995, Pharmacogenetics 5:121–141). Since reduced dopaminergic functions have been found in individuals with a minor A1 allele of the dopamine D2 receptor, it has been suggested that the dopamine D2 receptor may be a reinforcement or reward gene (Noble, 1994, Alcohol Supp. 2:35–43). Furthermore, several studies suggest that an associate of dopamine D2 receptor gene polymorphisms are associated with impulsive-addictive-compulsive behavior, i.e., “Reward Deficiency Syndrome” (reviewed by Blum et al., 1995, Pharmacogenetics 5:121–141).
U.S. Pat. No. 4,435,419 to Epstein et al. discloses racemic, (±)-1-(3,4-dichlorophenyl)-3-azabicyclo[3.1.0]hexane for use as an anti-depressant agent.
U.S. Pat. No. 6,204,284 to Beer et al. discloses racemic, (±)-1-(3,4-dichlorophenyl)-3-azabicyclo[3.1.0]hexane for use in the prevention or relief of a withdrawal syndrome resulting from addition to drugs and for the treatment of chemical dependencies.
Administration of a racemic, i.e., 50:50, mixture of the (+)- and the (−)-enantiomer of any drug, for example (±)-1-(3,4-dichlorophenyl)-3-azabicyclo[3.1.0]hexane, to a patient can be disadvantageous. First, the racemic mixture might be less pharmacologically active than one of its enantiomers, rendering racemic drugs inherently inefficient. Second, the racemic mixture may be more toxic to a patient than one of its enantiomers, so that administration of a racemic mixture can lead to undesirable side effects in a patient.
Accordingly, there is a clear need in the art for an enantiomer, the enantiomer being preferably substantially free of the corresponding opposite enantiomer, which would overcome one or both of the aforementioned disadvantages.
Citation of identification of any reference in Section 2 of this application is not to be construed as an admission that such reference is prior art to the present application.